Make some inner classes static (#9624)

Motivation:
Classes `AbstractHttp2StreamChannel.Http2StreamChannelConfig`
and `DnsNameResolver.AddressedEnvelopeAdapter` may be static:
it doesn't reference its enclosing instance.

Modification:
Add `static` modifier.

Result:
Prevents a possible memory leak and uses less memory per class instance.

codec-http2/src/main/java/io/netty/handler/codec/http2/AbstractHttp2StreamChannel.java

@@ -1013,7 +1013,7 @@ abstract class AbstractHttp2StreamChannel extends DefaultAttributeMap implements
      * window, without having to create a new {@link WriteBufferWaterMark} object whenever the flow control window
      * changes.
      */
-    private final class Http2StreamChannelConfig extends DefaultChannelConfig {
+    private static final class Http2StreamChannelConfig extends DefaultChannelConfig {
         Http2StreamChannelConfig(Channel channel) {
             super(channel);
         }

resolver-dns/src/main/java/io/netty/resolver/dns/DnsNameResolver.java

@@ -1327,7 +1327,7 @@ public class DnsNameResolver extends InetNameResolver {
         }
     }
 
-    private final class AddressedEnvelopeAdapter implements AddressedEnvelope<DnsResponse, InetSocketAddress> {
+    private static final class AddressedEnvelopeAdapter implements AddressedEnvelope<DnsResponse, InetSocketAddress> {
         private final InetSocketAddress sender;
         private final InetSocketAddress recipient;
         private final DnsResponse response;